• TensorFlow Basics

• R Interfaces to TensorFlow

• Deep Learning

• Supporting Tools

• Deployment

• Learning More

• Hardware independent
  • CPU (via C++ library Eigen)
  • GPU (via CUDA)
  • TPU (Tenor Processing Unit)
  • Others…

• Supports distributed execution and very large datasets

• Supports automatic differentiation

• A new general purpose numerical computing library!
  • Hardware independent
  • Distributed execution
  • Large datasets
  • Automatic differentiation

• Robust foundation for many deep learning applications

• TensorFlow models can be deployed with a low-latency C++ runtime

• R has a lot to offer as an interface language for TensorFlow

https://greta-dev.github.io/greta/

# Greta
theta = normal(0, 32, dim = 2)
mu <- alpha + beta * Z
X = normal(mu, sigma)
p <- ilogit(theta[1] + theta[2] * X)
distribution(y) = binomial(n, p)

# BUGS/JAGS
for(j in 1 : J) {
   y[j] ~ dbin(p[j], n[j])
   logit(p[j]) <- theta[1] + theta[2] * X[j]
   X[j] ~ dnorm(mu[j], tau)
   mu[j] <- alpha + beta * Z[j]
}
theta[1] ~ dnorm(0.0, 0.001)
theta[2] ~ dnorm(0.0, 0.001)

• Vector data—2D tensors of shape (samples, features)

• Timeseries or sequence data—3D tensors of shape (samples, timesteps, features)

• Images—4D tensors of shape (samples, height, width, channels) 

• Video—5D tensors of shape (samples, frames, height, width, channels)

head(data.matrix(iris), n = 10)

      Sepal.Length Sepal.Width Petal.Length Petal.Width Species
 [1,]          5.1         3.5          1.4         0.2       1
 [2,]          4.9         3.0          1.4         0.2       1
 [3,]          4.7         3.2          1.3         0.2       1
 [4,]          4.6         3.1          1.5         0.2       1
 [5,]          5.0         3.6          1.4         0.2       1
 [6,]          5.4         3.9          1.7         0.4       1
 [7,]          4.6         3.4          1.4         0.3       1
 [8,]          5.0         3.4          1.5         0.2       1
 [9,]          4.4         2.9          1.4         0.2       1
[10,]          4.9         3.1          1.5         0.1       1

• High-level R interfaces for neural nets and traditional models

• Low-level interface to allow enable new applications (e.g. Greta)

• Tools to faciliate productive workflow / experiment management

• Easy access to GPUs for training models

• Breadth and depth of educational resources

• High-level neural networks API capable of running on top of TensorFlow, CNTK, or Theano (and soon MXNet).

• Allows for easy and fast prototyping (through user friendliness, modularity, and extensibility).

• Supports both convolutional networks and recurrent networks, as well as combinations of the two.

• Runs seamlessly on CPU and GPU.

• https://keras.rstudio.com

model <- keras_model_sequential() %>%
  layer_conv_2d(filters = 32, kernel_size = c(3,3), activation = 'relu',
                input_shape = input_shape) %>% 
  layer_conv_2d(filters = 64, kernel_size = c(3,3), activation = 'relu') %>% 
  layer_max_pooling_2d(pool_size = c(2, 2)) %>% 
  layer_dropout(rate = 0.25) %>% 
  layer_flatten() %>% 
  layer_dense(units = 128, activation = 'relu') %>% 
  layer_dropout(rate = 0.5) %>% 
  layer_dense(units = 10, activation = 'softmax')

library(keras)

# Load MNIST images datasets (built in to Keras)
c(c(x_train, y_train), c(x_test, y_test)) %<-% dataset_mnist()

# Flatten images and transform RGB values into [0,1] range 
x_train <- array_reshape(x_train, c(nrow(x_train), 784))
x_test <- array_reshape(x_test, c(nrow(x_test), 784))
x_train <- x_train / 255
x_test <- x_test / 255

# Convert class vectors to binary class matrices
y_train <- to_categorical(y_train, 10)
y_test <- to_categorical(y_test, 10)

model <- keras_model_sequential()  %>% 
  layer_dense(units = 256, activation = 'relu', input_shape = c(784)) %>% 
  layer_dropout(rate = 0.4) %>% 
  layer_dense(units = 128, activation = 'relu') %>%
  layer_dropout(rate = 0.3) %>%
  layer_dense(units = 10, activation = 'softmax')

model %>% compile(
  loss = 'categorical_crossentropy',
  optimizer = optimizer_rmsprop(),
  metrics = c('accuracy')
)

history <- model %>% fit(
  x_train, y_train,
  batch_size = 128,
  epochs = 30,
  validation_split = 0.2
)

history

Trained on 48,000 samples, validated on 12,000 samples (batch_size=128, epochs=30)
Final epoch (plot to see history):
     acc: 0.9057
    loss: 1.5
 val_acc: 0.9317
val_loss: 1.088 

plot(history)

model %>% evaluate(x_test, y_test)

$loss
[1] 0.1078904

$acc
[1] 0.9815

model %>% predict_classes(x_test[1:100,])

  [1] 7 2 1 0 4 1 4 9 5 9 0 6 9 0 1 5 9 7 3 4 9 6 6 5 4 0 7 4 0 1 3 1 3 4 7
 [36] 2 7 1 2 1 1 7 4 2 3 5 1 2 4 4 6 3 5 5 6 0 4 1 9 5 7 8 9 3 7 4 6 4 3 0
 [71] 7 0 2 9 1 7 3 2 9 7 7 6 2 7 8 4 7 3 6 1 3 6 9 3 1 4 1 7 6 9

TODO: Deep learning section

• tfruns package

• cloudml package

• tfdeploy package

• Successful deep learning requires a huge amount of experimentation

• This requires a systematic approach to conducting and tracking the results of experiements

The training_run() function is like the source() function, but it automatically tracks and records output and metadata for the execution of the script:

library(tfruns)
training_run("mnist_mlp.R")

# define flags and their defaults
FLAGS <- flags(
  flag_integer("dense_units1", 128),
  flag_numeric("dropout1", 0.4),
  flag_integer("dense_units2", 128),
  flag_numeric("dropout2", 0.3)
)

# use flag 
layer_dropout(rate = FLAGS$dropout1)

# train with flag
training_run("mnist_mlp.R", flags = list(dropout1 = 0.3))

• Recommended reading

• Keras for R cheatsheet

• Gallery and examples

• Subscribe to the TensorFlow for R blog!

TensorFlow for R: https://tensorflow.rstudio.com

Stay up to date at: https://tensorflow.rstudio.com/blog/

Questions?

# Modify model object in place (note that it is not assigned back to)
model %>% compile(
  optimizer = 'rmsprop',
  loss = 'binary_crossentropy',
  metrics = c('accuracy')
)

• Keras models are directed acyclic graphs of layers whose state is updated during training.

• Keras layers can be shared by mutliple parts of a Keras model.